The present disclosure is generally related to scintillators and, more particularly, to scintillator compositions for detecting neutrons and methods of making the same.
Scintillator materials (hereinafter scintillators) are widely used in detectors for high-energy radiation, e.g. gamma rays, X-rays, cosmic rays, neutrons, and other particles characterized by an energy level of greater than or equal to about 1 keV. The scintillator is coupled with a light-detection means, such as, for example, a photosensor. When radiation impacts the scintillator, the scintillator emits light. The photosensor produces an electrical signal proportional to the number of light pulses received, and to their intensity. Scintillators are in common use for many applications. Examples include medical imaging equipment, e.g., positron emission tomography (PET) devices; well logging for the oil and gas industry; portable and hand-held detectors for homeland security; and various digital imaging applications.
In the detection of neutrons by solid-state scintillation, perhaps the most highly-utilized material stems from a granular mixture of 6-LiF and ZnS:Ag. Each component in this mixture represents “best-of-class” performance (i.e., respectively, neutron capture and luminescence). For neutron capture, the LiF crystal structure offers one of the highest Li site densities in the solid-state and therefore maximizes the probability of neutron interaction when enriched in 6-Li. For luminescence, ZnS:Ag is one of the brightest phosphors known and remains unparalleled in its emission under alpha and triton exposure (i.e., the by-products of 6-Li neutron capture). Thus, the combination of 6-LiF and ZnS:Ag, held together by an optically-transparent binding material (binder), forms a neutron scintillator composite (NSC) with exceptional efficiency.
Unfortunately, neutron scintillator composites, when comprised of such granular mixtures (e.g., 6-LiF/ZnS:Ag, 10-B2O3/ZnS:Ag, etc.), suffer from optical losses due to the scattering of light at internal interfaces and the absorption of light during transmission. The latter is aided by ZnS:Ag which can self-absorb its own luminescence. These loss mechanisms create a thickness limitation: increasing the NSC thickness beyond a certain threshold value (e.g., about 1.0 mm for 6-LiF/ZnS:Ag mixtures) provides no further light output despite the additional capability for neutron absorption. Thus, large continuous volumes are not accessible, and equally important, many useful shapes cannot be implemented without significant workarounds.